As shown by Webb et al. U.S. Pat. No. 4,340,545, assigned to the same assignee as the present invention and incorporated herein by reference, aromatic bis(ether anhydrides) were made by effecting an imide-anhydride exchange between aromatic bis(ether-N-organophthalimide) and phthalic anhydride in the presence of an imide-anhydride exchange catalyst and water. Recovery of the aromatic bis(ether anhydride) was achieved by extracting the aqueous imide-anhydride exchange reaction mixture with an inert organic solvent, such as toluene. Although valuable results have been achieved with the practice of the aforementioned method of Webb at al., it would be desirable to recover aromatic bis-(ether anhydride) without the employment of an organic solvent.
The present invention is based on the discovery that aromatic bis(ether anhydride) can be made by an imide-anhydride exchange reaction between aromatic bisimide and phthalic anhydride in the presence of an imide-anhydride exchange catalyst and water followed by the use of a vaporous mixture of water and the imide-anhydride exchange catalyst in a stripper-reactor, without the employment of an organic solvent.